Mapping schemes for secondary synchronization signal scrambling

ABSTRACT

Embodiments of the present disclosure provide a transmitter, a receiver and methods of operating a transmitter and a receiver. In one embodiment, the transmitter includes a synchronization unit configured to provide a primary synchronization signal and a secondary synchronization signal having first and second segments. The transmitter also includes a secondary scrambling unit configured to provide a scrambled secondary synchronization signal, wherein scrambling agents for the first and second segments are derived from a primary synchronization sequence of the primary synchronization signal. The secondary scrambling unit is further configured to provide an additional scrambling of one of the first and second segments, wherein a second scrambling agent is derived from the remaining segment of a secondary synchronization sequence of the secondary synchronization signal. The transmitter further includes a transmit unit configured to transmit the primary synchronization signal and the scrambled secondary synchronization signal.

CROSS-REFERENCE TO PROVISIONAL APPLICATIONS

This application is a continuation of application Ser. No. 12/140,789filed Jun. 17, 2008, now U.S. Pat. No. 8,054,823, and claims the benefitof U.S. Provisional Application No. 60/944,681 entitled “PSC to SSCScrambling Mapping” to Anand G. Dabak and Eko N. Onggosanusi filed onJun. 18, 2007, which is incorporated herein by reference in itsentirety.

This application also claims the benefit of U.S. Provisional ApplicationNo. 60/945,241 entitled “PSC to SSC Scrambling Mapping” to Anand G.Dabak and Eko N. Onggosanusi filed on Jun. 20, 2007, which isincorporated herein by reference in its entirety.

This application additionally claims the benefit of U.S. ProvisionalApplication No. 60/945,644 entitled “PSC to SSC Scrambling Mapping” toAnand G. Dabak, Eko N. Onggosanusi and Badri Varadarajan filed on Jun.22, 2007, which is incorporated herein by reference in its entirety.

This application further claims the benefit of U.S. ProvisionalApplication No. 60/954,692 entitled “PSC to SSC Scrambling Mapping” toAnand G. Dabak and Eko N. Onggosanusi filed on Aug. 8, 2007, which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure is directed, in general, to a communicationsystem and, more specifically, to a transmitter, a receiver and methodsof operating a transmitter and a receiver.

BACKGROUND

In a cellular network, such as one employing orthogonal frequencydivision multiple access (OFDMA), each cell employs a base station thatcommunicates with user equipment, such as a cell phone, a laptop, or aPDA, that is actively located within its cell. When the user equipmentis first turned on, it has to do an initial cell search in order to beconnected to the cellular network. This involves a downlinksynchronization process between the base station and the user equipmentwherein the base station sends a synchronization signal to the userequipment. In addition, as the moving user equipment approaches a cellboundary between two adjoining cells, it performs a neighboring cellsearch in preparation to handover its activation from the initial cellto the neighboring cell. Improvements in the synchronization processwould prove beneficial in the art.

SUMMARY

Embodiments of the present disclosure provide a transmitter, a receiverand methods of operating a transmitter and a receiver. In oneembodiment, the transmitter includes a synchronization unit configuredto provide a primary synchronization signal and a secondarysynchronization signal having first and second segments. The transmitteralso includes a secondary scrambling unit configured to provide ascrambled secondary synchronization signal wherein scrambling agents forthe first and second segments are derived from a primary synchronizationsequence of the primary synchronization signal. The secondary scramblingunit is further configured to provide an additional scrambling of one ofthe first and second segments, wherein a second scrambling agent isderived from the remaining segment of a secondary synchronizationsequence of the secondary synchronization signal. The transmitterfurther includes a transmit unit configured to transmit the primarysynchronization signal and the scrambled secondary synchronizationsignal.

In one embodiment, the receiver includes a receive unit configured toreceive a primary synchronization signal and a scrambled secondarysynchronization signal having even and odd segments. The receiver alsoincludes a primary synchronization unit configured to detect the primarysynchronization signal. The receiver further includes a secondarysynchronization unit configured to detect the scrambled secondarysynchronization signal having a scrambling agent for the even and oddsegments, wherein the scrambling agent is derived from a primarysynchronization sequence of the primary synchronization signal. Thesecondary synchronization unit is further configured to detect thescrambled secondary synchronization signal having an additionalscrambling of one of the even and odd segments, wherein a secondscrambling agent is derived from a remaining segment of a secondarysynchronization sequence of a secondary synchronization signal.

In another aspect, the method of operating the transmitter includesproviding a primary synchronization signal and a secondarysynchronization signal having first and second segments. The method ofoperating the transmitter also includes providing a scrambled secondarysynchronization signal, wherein scrambling agents for the first andsecond segments are derived from a primary synchronization sequence ofthe primary synchronization signal. The method of operating thetransmitter further includes further providing an additional scramblingof one of the first and second segments, wherein a second scramblingagent is derived from the remaining segment of a secondarysynchronization sequence of the secondary synchronization signal. Themethod of operating the transmitter still further includes transmittingthe primary synchronization signal and the scrambled secondarysynchronization signal.

In yet another aspect, the method of operating the receiver includesreceiving a primary synchronization signal and a scrambled secondarysynchronization signal having even and odd segments. The method ofoperating the receiver also includes detecting the primarysynchronization signal. The method of operating the receiver furtherinclude detecting the scrambled secondary synchronization signal havinga scrambling agent for the even and odd segments, wherein the scramblingagent is derived from a primary synchronization sequence of the primarysynchronization signal. The method of operating the receiver stillfurther includes further detecting the scrambled secondarysynchronization signal having an additional scrambling of one of theeven and odd segments, wherein a second scrambling agent is derived froma remaining segment of a secondary synchronization sequence of asecondary synchronization signal.

The foregoing has outlined preferred and alternative features of thepresent disclosure so that those skilled in the art may betterunderstand the detailed description of the disclosure that follows.Additional features of the disclosure will be described hereinafter thatform the subject of the claims of the disclosure. Those skilled in theart will appreciate that they can readily use the disclosed conceptionand specific embodiment as a basis for designing or modifying otherstructures for carrying out the same purposes of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, referenceis now made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates an exemplary diagram of an embodiment of a cellularnetwork constructed according to the principles of the presentdisclosure;

FIG. 2 illustrates a diagram of a downlink (transmit) radio frame thatincludes a downlink synchronization signal constructed according to theprinciples of the present disclosure;

FIG. 3A illustrates an embodiment of a primary synchronization signalconstructed according to the principles of the present disclosure;

FIG. 3B illustrates an embodiment of a scrambled secondarysynchronization signal (S-SCH) mapping based on employing two segmentsand constructed according to the principles of the present disclosure;

FIG. 4 illustrates a diagram of an embodiment of secondarysynchronization sequence scrambling constructed according to theprinciples of the present disclosure;

FIG. 5 illustrates a flow diagram of an embodiment of a method ofoperating a transmitter carried out in accordance with the principles ofthe present disclosure; and

FIG. 6 illustrates a flow diagram of an embodiment of a method ofoperating a receiver carried out in accordance with the principles ofthe present disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary diagram of an embodiment of a cellularnetwork 100 constructed according to the principles of the presentdisclosure. The cellular network 100 is part of an OFDMA system andincludes a cellular grid having a centric cell and six surroundingfirst-tier cells. The centric cell employs a centric base station(NodeB), as shown.

The NodeB includes a base station transmitter 105 having asynchronization unit 106, a secondary scrambling unit 107 and a transmitunit 108. The cellular network 100 also includes user equipment (UE)operating within the centric cell, wherein the NodeB acts as a servingbase station to the UE. The UE includes a UE receiver 110 having areceive unit 111, a primary synchronization unit 112 and a secondarysynchronization unit 113.

In the base station transmitter 105 the synchronization unit 106 isconfigured to provide a primary synchronization signal and a secondarysynchronization signal having first and second segments. The secondaryscrambling unit 107 is configured to provide a scrambled secondarysynchronization signal wherein scrambling agents for the first andsecond segments are derived from a primary synchronization sequence ofthe primary synchronization signal. In one embodiment, the secondaryscrambling unit 107 is further configured to provide an additionalscrambling of one of the first and second segments, wherein a secondscrambling agent is derived from the remaining segment of a secondarysynchronization sequence of the secondary synchronization signal. Thetransmit unit 108 is configured to transmit the primary synchronizationsignal and the scrambled secondary synchronization signal.

In the UE receiver 110, the receive unit 111 is configured to receivethe primary synchronization signal and the scrambled secondarysynchronization signal having even and odd segments, and the primarysynchronization unit 112 is configured to detect the primarysynchronization signal. The secondary synchronization unit 113 isconfigured to detect the scrambled secondary synchronization signalhaving a scrambling agent for the even and odd segments, wherein thescrambling agent is derived from a primary synchronization sequence ofthe primary synchronization signal.

In one embodiment, the secondary synchronization unit 113 is furtherconfigured to detect the scrambled secondary synchronization signalhaving an additional scrambling of one of the even and odd segments,wherein a second scrambling agent is derived from a remaining segment ofa secondary synchronization sequence of the secondary synchronizationsignal.

FIG. 2 illustrates a diagram of a downlink (transmit) radio frame 200that includes a downlink synchronization signal constructed according tothe principles of the present disclosure. The downlink radio frame 200may be employed in a cellular network, such as the cellular network 100of FIG. 1, and includes two synchronization signals 205, 210 whereineach consists of a primary synchronization signal (also referred to asP-SCH) 205 a or 210 a and a secondary synchronization signal (alsoreferred to as S-SCH) 205 b or 210 b that are located as shown. OneP-SCH 205 a or 210 a and one corresponding S-SCH 205 b or 210 b symbolare transmitted every 5 ms epoch, as shown. Design of thesynchronization signals to enable fast cell search is required forlong-term evolution (LTE) of 3 GPP.

An underlying representation for the P-SCH 205 a or 210 a is called aprimary synchronization signal (PSS), which corresponds to a primarysynchronization code (PSC) or sequence. The PSS for each cell is chosenfrom three sequences and is tied to the cell identity (ID) within acertain group of cell IDs. Hence, the PSS conveys partial cell IDinformation and one PSS symbol carries three cell ID hypotheses. Anunderlying representation for the S-SCH 205 b or 210 b is called asecondary synchronization signal (SSS), which corresponds to a secondarysynchronization code (SSC) or sequence. The SSS 205 b or 210 b carriescell-specific information. The following cell-specific information maybe carried in one SSS symbol.

A total of 504 cell IDs are supported in LTE. Since three cell IDhypotheses are carried in the PSS 205, 168 cell ID groups (168hypotheses) are provided. Additionally, since there are two SSS symbolsper radio frame 200 (one in the first subframe (subframe 0), and anotherone in the sixth subframe (subframe 5), a radio frame timing indicator(2 hypotheses) is also provided. In some embodiments, a frequencyhopping indicator for a downlink reference signal (2 hypotheses) may beprovided that indicates if frequency hopping is employed within theradio frame 200. Additionally, an antenna configuration of transmitter(TX) diversity indicator (2 or 3 hypotheses) may also be provided thatindicates either the antenna configuration or TX diversity employed bythe broadcast channel (BCH).

The SSS may be detected coherently (by using the PSS as a phasereference) or non-coherently (without phase reference). This option isconsidered for the SSS in the following embodiments. In general,coherent detection yields better performance. Additionally, atwo-segment SSS is employed where two groups of M-sequences withhalf-length (31) may be used to construct a large number of compositesequences. The two sequences may be either interleaved or staggered.

FIG. 3A illustrates an embodiment of a primary synchronization signal300 constructed according to the principles of the present disclosure.FIG. 3A shows a mapping in the frequency domain of a PSS correspondingto the primary synchronization signal (PSS) 300 that occupies a center63 sub-carriers, as shown. The mapping also includes a DC sub-carrierand the data sub-carriers. This mapping assumes that there are 31sub-carriers to both the left and right of the DC sub-carrier.

Since coherent SSS detection offers better performance than non-coherentdetection in most scenarios, the PSS and SSS designs accommodateaccurate coherent SSS detection. Additionally, since the PSS is used asa phase reference (to provide channel estimates) for decoding the SSS(demodulating the SSS), the SSS occupies exactly the same set ofsub-carriers as the PSS in the illustrated embodiment.

FIG. 3B illustrates an embodiment of a scrambled secondarysynchronization signal (SSS) mapping 350 based on employing two segmentsand constructed according to the principles of the present disclosure.The SSS mapping 350 occupies the center 63 sub-carriers as discussedwith respect to FIG. 3A. The mapping includes the DC sub-carrier 301 anddata sub-carriers, as before. Here, the mapping shows an interleaving ofsub-carriers representing even and odd scrambled sequences of atwo-segment, interleaved SSS.

In this case, the underlying SSS is of length-31 (two length-31sequences interleaved in the frequency domain). Several naturalcandidates are M-sequences (pseudo noise (PN) sequences), Goldsequences, and truncated Walsh sequences. With Walsh sequences, theunderlying length is 32, with one sample truncated. Other designs arealso possible.

Referring again to FIG. 1, the following concerns and issues areaddressed by embodiments of the present disclosure. For a two-level ortwo-segment design of the SSS, different SSS approaches may beconsidered for LTE. For example, consider two identical sets of 32Walsh-Hadamard codes of length 32 or 31 each wherein a product of thetwo code sets is taken to generate potentially 1024 codes. Then, either340 or 680 SSCs may be chosen. Thus, the SSCs are given by {W_(i),W_(j)} where i=1, . . . , 32, j−1, . . . , 32, and each of the {W_(i)};i=1, . . . , 32 and {W_(j)}; j=1, . . . , 32 are identical sets ofWalsh-Hadamard codes. Let each code {W_(i)}, be given by {w_(i) ¹, . . ., w_(i) ^(l), . . . , w_(i) ^(L)}; and an element w/ε{0, 1}. Normally 32Walsh-Hadamard codes may be considered, wherein their length is 32.However, the last bit can be punctured, to get a length 31 code from thelength 32 Hadamard code.

Another approach is to start with a length 31 Pseudo Noise (PN) code C.Then consider the 31 cyclic shifts of this code. Let the cyclic shift ofk of the code C be denoted by C_(k). Now consider the set of thesecyclic shifted codes {C_(k)}; k=1,2, . . . , 31 and again construct 961codes by {C_(i), C_(j)}; i=1, . . . , 31 and j=1, . . . , 31. Again, 340or 680 codes out of these may be used for SSCs.

One problem is that if the above structure is employed for SSC design,then it has a drawback when one or more base stations are interferingwith a given base station. Let {W_(i) ₁ , W_(j) ₁ } be the SSC set of afirst base station and {W_(i) ₂ , W_(j) ₂ } be the SSC set of a secondbase station. In this case, when the second base station is interferingwith the first base station, a mobile user at the cell boundary of thefirst and second base stations could also confuse the above code sets to{W_(i) ₁ , W_(j) ₂ } and {W_(i) ₂ , W_(j) ₁ }. If the mobile userdetects these code sets, then it would indeed be locking onto a basestation which is not in the vicinity, and it would be a long processbefore the mobile user realizes this.

Embodiments of the present disclosure provide an SSC design thatinvolves a scrambling code on the code set {W_(j)} wherein thescrambling code is a function of the first code set {W_(i)}. Let{V_(i)}; i=1, . . . , 32 (in a Walsh code case) be the scrambling codeswherein each of which V_(i) is associated with W_(i). Again, each code{V_(i)}, is given by {V_(i) ¹, . . . , V_(i) ^(l), . . . , V_(i) ^(L)};and an element V_(i) ^(l)ε{0, 1}.

Similarly, letW _(j) {circle around (×)}V _(i)={w_(j) ¹v_(i) ¹, . . . , w_(j)^(L)v_(j) ^(L)}  (1)denote the scrambling of code {W_(j)} by code {V_(i)}. Similarly, thescrambling of the PN codes {C_(j)} can be defined.

There are several options for embodiments of the present disclosure. Forconvenience of notation, the embodiments assuming Walsh code based SSSdesigns, given above, are presented. However it is understood that thesame design can also be extended to the PN code or M-sequence based SSSdesign or any other two-segment SSS design.

For embodiments related to a first option, the above given code designis accepted, namely the codes are represented as {W_(i), V_(i){circlearound (×)}W_(j)}. A typical receiver for detecting the code set {W_(i),W_(j)} will do a Walsh Hadamard transform of the code set {W_(i)} andthe code set {W_(j)} separately. Then it will sum up the correlationoutput of these code sets over all combinations to generate thecorrelation output for the code set {W_(i), W_(j)}.

On the other hand, when there is scrambling used on the second segment,the mobile has to use as many Walsh transforms for the set V_(i){circlearound (×)}W_(j) as the number of codes in set W_(i). Thus, instead ofneeding only two Walsh transforms for the code set {W_(i), W_(j)}, themobile will need (one plus the number of codes in set {W_(i)}) 33 in theworst case. Thus the complexity of the Walsh transforms has increased 16times.

A technique is employed by which the number of Walsh transforms can bereduced while still maintaining the advantage of code randomization. Thecode set {V_(j)} is divided into three groups {V_(i) ¹, V_(i) ², V_(i)³} wherein each group corresponds to a PSC. For a given PSC, thescrambling codes would then be used only from the group corresponding tothat particular PSC. The groups can be decided by a pre-existing mappingbetween the code set {W_(i)} for a given PSC.

For example, for a first PSC the group may consist of only thescrambling code {V1, . . . , V10}, implying that a given {W_(i)} ismapped to {V_(mod) ₁₀ _((i))}. Similarly for a second PSC, the group{W_(i)} can be mapped to {V_(10+mod) ₁₀ _((i))}, and for a third PSC, itis mapped to {V_(20+mod) ₁₀ _((i))}. The advantage of tying the PSC tothe group of scrambling codes is that only one third of the WalshHadamard transforms are needed for SSC detection, thereby reducing thecomplexity of the SSC detection. Note that this scheme still results ininterference from the neighboring base stations. This is because theneighboring base stations will be assigned different PSCs.

For embodiments related to a second option, the code set {W_(i)} ispartitioned into M groups. Namely, m={1, 2, . . . , M} such that for agiven i there is a single m in this set (i.e., a many to one mapping).Let the number of PSCs possible be P that is denoted with a variable p;p=1,2, . . . , P and pick

≦P. Then the code set {V_(i)} has

*M elements (the

=3 corresponding to the three PSCs in the case of LTE). Then, a givenW_(i) in the first segment of SSC for a given PSC p employsV_(m+(p−1)*M) for scrambling the code W_(j) on the second segment.

In the particular case where M=1 (i.e., there is a single set in whichthe {W_(i)} is partitioned) and

=3 (i.e., there are three PSCs), there are only three scrambling codesused. Other variations that are possible are, M=9 and

=3. Yet another variation is that instead of having concrete mappinglike {V_(m+(p−1)*M) } for a given p and a given m, there is a mapping toan index i for code V_(i) which is used as a scrambling code for W_(j).This mapping may be stored in a look-up table in the base station andthe mobile.

Embodiments related to a third option, involve also having a scramblingcode on the first segment of the codes and further having thisscrambling tied to the PSCs. The reason for introducing this scramblingon the first SSC segment is because, on the cell boundary (sectorboundary), the mobile will receive SSC from multiple sectors or cells ofthe same base station. In the absence of scrambling on the firstsegment, the channel estimate for coherent detection obtained from thePSC, which is common to all the cells or sectors of a given basestation, will not appropriately reflect the channel estimate of thefirst segment of the SSCs.

The resulting scrambling on the first segment can now be indicated as {

{circle around (×)}W_(i), W_(j)}. Since the scrambling is linked to thePSC, there are only three scrambling codes for

. Another variation of the invention would then be where the scramblingis present on both the first segment as given in this current option, oralso on the second segment as given in the first and second optionsabove.

For embodiments related to a fourth option, a first variation relates tothe selection of the 340 or so codes discussed above. M1 and M2 aredefined as the number of codes that are used for the first and secondsegments of the SSC, respectively. There are two ways in which thesecodes can be selected. Pick M1 of the 31 length-31 codes defined abovefor W_(i), and pick M2 of the 31 length-31 codes for W_(j) such thatM1*M2 is an integer greater than 340. If M1=18 and M2=19 are picked,this condition is satisfied with M1*M2=342.

This gives a balanced number of codes for the first and second segmentsof the SSC. Similarly for M2=31 and M1=11, M1*M2−341. For thiscombination of (M1, M2), any of the scrambling schemes given in thefirst, second and third options can be used. One such embodiment is asfollows.

The first segment of the SSC is scrambled by a code corresponding to thePSC as in the third option. The second segment of the SSC is scrambledby one of the following alternatives.

(i) Employ a combination of PSC-dependent scrambling (it may be the sameor different from that used in the first segment of the SSC) and ascrambling code V_(i) on the second segment of SSC which is dependent onthe first segment of the SSC (analogous to the second option). In thiscase,

=3. Note that V_(i) may have a one-to-one correspondence with the firstsegment of the SSC (i.e., no grouping is used) or a one-to-manycorrespondence (i.e., grouping is used).

(ii) Employ a scrambling code V_(i) on the second segment of SSC, whichis dependent on the first segment of the SSC (analogous to the secondoption) without any PSC-dependent scrambling. In this case,

=1. Note that V_(i) may have a one-to-one correspondence with the firstsegment of the SSC (i.e., no grouping used) or a one-to-manycorrespondence (i.e., grouping is used).

(iii) Employ a PSC-dependent scrambling (different from that used in thefirst segment of the SSC) without the SSC-dependent scrambling of thefirst option. This can be viewed as a combination of the first and thirdoptions.

The embodiment with M1=11 and M2=31 is better from an implementationperspective because there are only 11 combinations for M2=31 code set of{W_(j)}. Note that any other combination of (M1,M2) is also possible.

A second variation of the fourth option is related to the selection ofthe above 170 or so codes. This is relevant for the SSC structure wherethe first-segment and second-segment code set assignment is swappedacross the two sub-frames within one radio frame. M1 and M2 are definedas the number of codes that are used for the first and second segmentsof the SSC, respectively. There are two ways in which these codes can beselected. Pick M1 of the 31 length-31 codes defined above for W_(i), andpick M2 of the 31 length-31 codes for W_(j) such that M1*M2 is aninteger greater than 170.

If M1=13 and M2=14 are picked, this condition is satisfied withM1*M2=182. This gives a balanced number of codes for the first andsecond segments of the SSC. Similarly for M2=31 and M1=6, M1*M2=186. Forthis combination of (M1, M2), any of the scrambling schemes give in thefirst, second and third options can be used. One such embodiment is asfollows:

The first segment of the SSC is scrambled by a code corresponding to thePSC as presented in the third option. The second segment of the SSC isscrambled by one of the following alternatives.

(i) Employ a combination of PSC-dependent scrambling (it may be the sameor different from that used in the first segment of the SSC) and ascrambling code V_(i) on the second segment of the SSC, which isdependent on the first segment of the SSC (analogous to the secondoption). In this case,

=3. Note that V_(i) may have a one-to-one correspondence with the firstsegment of the SSC (i.e., no grouping is used) or a one-to-manycorrespondence (i.e., grouping is used).

(ii) Employ a scrambling code V on the second segment of the SSC, whichis dependent on the first segment of the SSC (analogous to the secondoption) without any PSC-dependent scrambling. In this case,

=1. Note that V_(i) may have a one-to-one correspondence with the firstsegment of the SSC (i.e., no grouping is used) or a one-to-manycorrespondence (i.e., grouping is used).

(iii) Employ a PSC-dependent scrambling (different from that used in thefirst segment of the SSC) without an SSC-dependent scrambling of thefirst option. This can be viewed as a combination of the first and thirdoptions. Note that any other combination of (M1, M2) is also possible.

For embodiments related to a fifth option, the scrambling code design isaddressed. For the sake of clarity, the net scrambling code design forboth the Walsh code based SSC and the PN code based SSC are given. Inthe Walsh code based SSC, rotation of a given base sequence with goodauto-correlation properties is used. In particular, the base sequencecan be a Golay sequence of length 31/32, or it can also be the rotatedPN sequence {C_(i)}. These rotated sequences may be used as thescrambling codes for the Walsh code based SSC. Thus, the scrambling code{V_(i)}={C_(i)}. The chosen PN code or M-sequence can be any of the onesgiven in Table 1 below.

For PN code based SSC, let B be another PN code of length-31. Note thatthere are six PN sequences of length-31. The six PN codes are given inTable 1 below. In this case, the scrambling code is used as a rotated PNsequence, which is different from the rotated PN sequence for the SSC.

TABLE 1 PN sequences of length-31 Code Code Code Code Code Code 1 2 3 45 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 1 1 0 01 0 0 0 1 1 1 1 0 1 1 0 0 0 1 0 0 1 0 1 0 1 1 1 1 1 0 0 0 1 1 0 1 0 1 00 0 1 1 0 1 1 1 1 0 0 1 1 1 1 0 0 0 1 1 1 0 1 0 1 1 0 1 1 0 1 1 1 0 1 10 0 1 1 0 1 1 0 1 1 1 1 0 0 0 1 1 1 0 1 0 1 1 1 0 1 0 1 1 0 1 0 1 0 1 00 1 0 1 0 1 0 1 1 1 0 1 1 1 0 0 1 0 0 0 1 0 0 1 1 1 1 1 0 0 0 0 0 1 1 01 1 1 1 1 1 1 0

FIG. 4 illustrates a diagram 400 of an embodiment of secondarysynchronization sequence scrambling constructed according to theprinciples of the present disclosure. The diagram 400 includes first andsecond SSS segments as may be employed in subframes 0 and 5 of FIG. 2above (indicated by m0 and m1, respectively). In subframe 0, the firstSSS segment is provided as an even sequence, and in subframe 5, it isprovided as an odd sequence, as shown. Correspondingly, in subframe 5,the second SSS segment is provided as an even sequence, and in subframe0, it is provided as an odd sequence, as shown. This action causes theswapping of the two SSS sequences in subframes 0 and 5, whichcorresponds to the first variation of the fourth option discussed above.

Each of the even and odd sequences is initially scrambled whereinscrambling agents for both employ a PSS corresponding to PSS segments insubframes 0 and 5 of FIG. 2. This corresponds to the third optiondiscussed above. Then, an additional scrambling of each of the oddsequences is provided by a second scrambling agent employing thecorresponding even SSS of each subframe, as shown. In one embodiment,the second scrambling agent may also correspond to one of a number ofgroups in the corresponding even SSS, wherein the number of groups isequal to eight. This corresponds to a combination of the first andsecond options discussed above. The resulting even and odd scrambledsequences are interleaved as shown in FIG. 3B above.

FIG. 5 illustrates a flow diagram of an embodiment of a method ofoperating a transmitter 500 carried out in accordance with theprinciples of the present disclosure. The method 500 is for use with abase station in an OFDMA system and starts in a step 505. Then, aprimary synchronization signal and a secondary synchronization signalhaving first and second segments are provided, in a step 510. In oneembodiment, the primary synchronization sequence is a length-31sequence. Additionally, the primary synchronization sequence is derivedfrom an M-sequence.

A scrambled secondary synchronization signal, wherein scrambling agentsfor the first and second segments are derived from a primarysynchronization sequence of the primary synchronization signal isprovided in a step 515. In one embodiment, an additional scrambling ofone of the first and second segments, wherein a second scrambling agentis derived from the remaining segment of a secondary synchronizationsequence of the secondary synchronization signal is further provided ina step 520.

In one embodiment, the second scrambling agent is the first segmentemployed in a first subframe of a transmit radio frame having 10subframes. Additionally, the second scrambling agent is the secondsegment employed in a sixth subframe of the transmit radio frame having10 subframes.

In one embodiment, the second scrambling agent corresponds to one of anumber of groups in the remaining segment of the secondarysynchronization sequence. Correspondingly, the number of groups iseight. The scrambled secondary synchronization signal provides even andodd scrambled sequences that are interleaved. Additionally, thescrambled secondary synchronization signal provides even and oddscrambled segments that are each length-31 sequences. The primarysynchronization signal and the scrambled secondary synchronizationsignal are transmitted in a step 525. The method 500 ends in a step 530.

FIG. 6 illustrates a flow diagram of an embodiment of a method ofoperating a receiver 600 carried out in accordance with the principlesof the present disclosure. The method 600 is for use with user equipmentin an OFDMA system and starts in a step 605. Then, a primarysynchronization signal and a scrambled secondary synchronization signalhaving even and odd segments are received in a step 610. The primarysynchronization signal is detected in a step 615.

The scrambled secondary synchronization signal having a scrambling agentfor the even and odd segments is detected in a step 620, wherein thescrambling agent is derived from a primary synchronization sequence ofthe primary synchronization signal. In one embodiment, the primarysynchronization sequence is a length-31 sequence. Additionally, theprimary synchronization sequence is derived from an M-sequence.

In one embodiment, the scrambled secondary synchronization signal isfurther detected in a step 625 that has an additional scrambling of oneof the even and odd segments, wherein a second scrambling agent isderived from a remaining segment of a secondary synchronization sequenceof a secondary synchronization signal.

In one embodiment, the second scrambling agent is the first segmentemployed in a first subframe of a transmit radio frame having 10subframes. Correspondingly, the second scrambling agent is the secondsegment employed in a sixth subframe of a transmit radio frame having 10subframes.

In one embodiment, the second scrambling agent corresponds to one of anumber of groups in the remaining segment. Correspondingly, the numberof groups is eight. The scrambled secondary synchronization signalprovides even and odd sequences that are interleaved. Additionally, theeven and odd sequences are each length-31 sequences. The method 600 endsin a step 630.

While the methods disclosed herein have been described and shown withreference to particular steps performed in a particular order, it willbe understood that these steps may be combined, subdivided, or reorderedto form an equivalent method without departing from the teachings of thepresent disclosure. Accordingly, unless specifically indicated herein,the order or the grouping of the steps is not a limitation of thepresent disclosure.

Those skilled in the art to which the disclosure relates will appreciatethat other and further additions, deletions, substitutions andmodifications may be made to the described example embodiments withoutdeparting from the disclosure.

1. A transmitter, comprising: a synchronization unit configured toprovide a primary synchronization signal and a secondary synchronizationsignal having first and second segments; a secondary scrambling unitconfigured to provide a scrambled secondary synchronization signalwherein at least one scrambling agent for the first or second segment isderived from a primary synchronization sequence of the primarysynchronization signal; and a transmit unit configured to transmit theprimary synchronization signal and the scrambled secondarysynchronization signal.
 2. The transmitter as recited in claim 1 whereinthe primary synchronization sequence is a length-31 sequence.
 3. Thetransmitter as recited in claim 1 wherein the primary synchronizationsequence is derived from an M-sequence.
 4. The transmitter as recited inclaim 1 further configured to provide an additional scrambling of one ofthe first and second segments, wherein a second scrambling agent isderived from the remaining segment of a secondary synchronizationsequence of the secondary synchronization signal.
 5. The transmitter asrecited in claim 4 wherein the second scrambling agent is the firstsegment employed in a first subframe of a transmit radio frame having 10subframes.
 6. The transmitter as recited in claim 4 wherein the secondscrambling agent is the second segment employed in a sixth subframe of atransmit radio frame having 10 subframes.
 7. The transmitter as recitedin claim 4 wherein the second scrambling agent corresponds to one of anumber of groups in the remaining segment.
 8. The transmitter as recitedin claim 4 wherein the scrambled secondary synchronization signalprovides even and odd scrambled sequences that are interleaved.
 9. Thetransmitter as recited in claim 4 wherein the scrambled secondarysynchronization signal provides even and odd scrambled segments that areeach length-31 sequences.
 10. A method of operating a transmitter,comprising: providing a primary synchronization signal and a secondarysynchronization signal having first and second segments; providing ascrambled secondary synchronization signal wherein scrambling agents forthe first or second segment is derived from a primary synchronizationsequence of the primary synchronization signal; and transmitting theprimary synchronization signal and the scrambled secondarysynchronization signal.
 11. The method as recited in claim 10 whereinthe primary synchronization sequence is a length-31 sequence.
 12. Themethod as recited in claim 10 wherein the primary synchronizationsequence is derived from an M-sequence.
 13. The method as recited inclaim 10 further providing an additional scrambling of one of the firstand second segments, wherein a second scrambling agent is derived fromthe remaining segment of a secondary synchronization sequence of thesecondary synchronization signal.
 14. The method as recited in claim 13wherein the second scrambling agent is the first segment employed in afirst subframe of a transmit radio frame having 10 subframes.
 15. Themethod as recited in claim 13 wherein the second scrambling agent is thesecond segment employed in a sixth subframe of a transmit radio framehaving 10 subframes.
 16. The method as recited in claim 13 wherein thesecond scrambling agent corresponds to one of a number of groups in theremaining segment of the secondary synchronization sequence.
 17. Themethod as recited in claim 13 wherein the scrambled secondarysynchronization signal provides even and odd scrambled sequences thatare interleaved.
 18. The method as recited in claim 13 wherein thescrambled secondary synchronization signal provides even and oddscrambled segments that are each length-31 sequences.
 19. A receiver,comprising: a receive unit configured to receive a primarysynchronization signal and a scrambled secondary synchronization signalhaving at least one even or odd segment; a primary synchronization unitconfigured to detect the primary synchronization signal; and a secondarysynchronization unit configured to detect the scrambled secondarysynchronization signal having a scrambling agent for the even and oddsegments, wherein the scrambling agent is derived from a primarysynchronization sequence of the primary synchronization signal.
 20. Amethod of operating a receiver, comprising: receiving a primarysynchronization signal and a scrambled secondary synchronization signalhaving at least one even or odd segment; detecting the primarysynchronization signal; and detecting the scrambled secondarysynchronization signal having a scrambling agent for the even and oddsegments, wherein the scrambling agent is derived from a primarysynchronization sequence of the primary synchronization signal.